The main objectives of the proposed research are: to elucidate the mechanism(s) by which the dialdehyde derivative of adenine nucleoside and nucleotides inhibit nucleic acid synthesis in Leukemia L1210 tumor cells; and to determine the specificity of this inhibition by studying the dialdehyde derivatives of the other purine and pyrimidine nucleosides and nucleotides. The study will be carried out on selected enzymes involved with nucleic acid synthesis in cell-free extracts, in intact tumor cells in culture and on tumor growth in vivo.